1. Field of the Invention
The present invention relates to a stencil printing machine in which a stencil sheet already subjected to a stencil making process is wound around a rotary cylindrical drum for printing, and also relates to a wrinkle preventing method for a stencil sheet of the stencil printing machine.
The present application is based on Japanese Patent Application No. 2000-057403, which is incorporated herein by reference.
2. Description of the Related Art
Generally, a stencil printing machine includes a rotary cylindrical drum, which has an ink-permeable circumferential wall having a porous structure, and which can be rotated about its own axis. A stencil sheet, which has been subjected to a stencil making process, is wound around the outer peripheral surface of the circumferential wall. The rotary cylindrical drum contains an ink supplying device for supplying ink to the outer peripheral surface of the circumferential wall so as to allow the ink to pass through. Further, a press roller, that can come in contact with the outer peripheral surface of the circumferential wall, is placed outside of the rotary cylindrical drum. A printing sheet is supplied to a gap between the rotary cylindrical drum and the press roller in synchronization with rotation of the rotary cylindrical drum and the printing sheet is pressed by the press roller against the stencil sheet wound around the rotary cylindrical drum, whereby ink is passed through the perforated portions in the stencil sheet and is transferred to the printing sheet for printing.
When printing terminates and new printing is started, the used stencil sheet previously wound around the rotary cylindrical drum is peeled off and discharged and a newly-made stencil sheet is wound around the rotary cylindrical drum, whereby printing is performed in a similar manner to that described above.
However, with the stencil printing machine in the related art, when the used stencil sheet is discharged, the ink existing between the peeled-off stencil sheet and the outer peripheral surface of the circumferential wall is burst. As shown in FIG. 10A, ink 101 is drawn out onto the outer peripheral surface of a circumferential wall 100 of a rotary cylindrical drum so that the ink 101 is napped from holes 100a in the circumferential wall 100 by peeling off a stencil sheet M. Accordingly, the ink 101 is put sparsely on the outer peripheral surface of the circumferential wall 100.
In the state shown in FIG. 10A, if a newly-made stencil sheet M is wound around the circumferential wall 100, spaces S occur between the outer peripheral surface of the circumferential wall 100 and the stencil sheet M, as shown in FIG. 10B. At the printing, the spaces S become air layers Sxe2x80x2, causing the attached stencil sheet M to be wrinkled so that an image appearing on a printing sheet is influenced.
FIGS. 11A to 11D show a process (print process) in which the circumferential wall 100 onto which the stencil sheet M is attached is developed into a plane in the state in which the spaces S (air layers Sxe2x80x2) occur as mentioned above and a press roller 12 presses with rotation of the rotary cylindrical drum.
As shown in FIGS. 11A and 11B, when the press roller 102 presses along the move direction of the circumferential wall 100 as the rotary cylindrical drum is rotated, the air layers Sxe2x80x2 are built up to a mass, which is carried away downstream of the stencil sheet M. As shown in FIGS. 11C and 11D, the air layer Sxe2x80x2 mass is discharged from a part of the downstream end of the stencil sheet M. Thus, the portion not uniformly carried away by the press roller 102, namely, the portion of the stencil sheet M swollen by the air layer Sxe2x80x2 mass is crushed and broken by the press roller 102 to produce wrinkles 103.
The air layers Sxe2x80x2 easily occur particularly if there is used a low-rigidity stencil sheet easy to break or a stencil sheet made at a high closed density based on an original of a low perforation rate.
It is therefore an object of the present invention to provide a stencil printing machine for making it possible to eliminate air layers occurring between an attached stencil sheet and a circumferential wall for preventing the stencil sheet from being wrinkled, and a wrinkle preventing method on a stencil sheet of the stencil printing machine.
To achieve the above object, according to a first aspect of the present invention, there is provided a stencil printing machine which comprises a rotary cylindrical drum rotatable about its own axis, the rotary cylindrical drum including an ink-permeable cylindrical circumferential wall having an outer peripheral surface around which a stencil sheet subjected to a stencil making process can be wound; a contact member capable of contacting with an inner peripheral surface of the circumferential wall, the contact member being disposed in the rotary cylindrical drum; and a move mechanism capable of moving the contract member to a contact position at which the contact member is brought into contact with the inner peripheral surface of the circumferential wall or a distance position at which the contact member is spaced with a predetermined interval from the inner peripheral surface of the circumferential wall, wherein when the stencil sheet is not wound around the circumferential wall of the rotary cylindrical drum, the rotary cylindrical drum is rotated while the contact member is placed at the contact position relative to an ink permeable portion of the circumferential wall.
As described above, the stencil printing machine according to the present invention includes the contact member that can be moved to the contact position with or the distance position from the inner peripheral surface of the circumferential wall in the rotary cylindrical drum. The contact member is placed at the contact position with the ink permeable portion of the circumferential wall and the rotary cylindrical drum is rotated in a state in which the stencil sheet is not wound around the rotary cylindrical drum, whereby ink drawn out through the ink permeable portion of the circumferential wall to the outer peripheral surface thereof because of peeling off the stencil sheet in the stencil discharging operation is pulled into the ink permeable portion of the circumferential wall by negative pressure produced by the contact member coming in contact with the inner peripheral surface of the circumferential wall and is removed. Therefore, if a newly-made stencil sheet is attached onto the outer peripheral surface of the circumferential wall, air layers are not produced between the outer peripheral surface of the circumferential wall and the stencil sheet. Thus, in a printing operation, the stencil sheet attached onto the rotary cylindrical drum can be prevented from being wrinkled, and a desired print image can be printed on a printing sheet without any wrinkles.
According to a second aspect of the present invention, the contact member may include an ink supplying roller which supplies ink to the inner peripheral surface of the circumferential wall.
In the stencil printing machine as recited in the second aspect of the present invention, the contact member is implemented as an ink supplying roller for supplying ink to the inner peripheral surface of the circumferential wall, so that the stencil sheet can be prevented from being wrinkled using the already existing configuration of stencil printing machine.
Of course, according to a third aspect of the present invention, to achieve the above object, there may be provided a wrinkle preventing method for preventing a wrinkle on a stencil sheet. In this case, the method may comprise the step of providing a stencil printing machine which includes a rotary cylindrical drum rotatable about its own axis, the rotary cylindrical drum including an ink-permeable cylindrical circumferential wall having an outer peripheral surface around which a stencil sheet subjected to a stencil making process can be wound; a contact member capable of contacting with an inner peripheral surface of the circumferential wall, the contact member being disposed in the rotary cylindrical drum; and a move mechanism capable of moving the contract member to a contact position at which the contact member is brought into contact with the inner peripheral surface of the circumferential wall or a distance position at which the contact member is spaced with a predetermined interval from the inner peripheral surface of the circumferential wall, and further comprise the steps of discharging the stencil sheet from the rotary cylindrical drum so that the rotary cylindrical drum is placed in a state in which the stencil sheet is not wound around the circumferential wall of the rotary cylindrical drum; rotating the rotary cylindrical drum while placing the contact member at the contact position relative to an ink permeable portion of the circumferential wall; placing the contact member at the distance position relative to the ink permeable portion of the circumferential wall; and winding, around the outer peripheral surface of the circumferential wall of the rotary cylindrical drum, a stencil sheet subjected to the stencil making process.
Accordingly, in the process from the stencil discharging operation to the stencil attaching operation, ink drawn out through the ink permeable portion of the circumferential wall to the outer peripheral surface thereof can be removed and the stencil sheet can be prevented from being wrinkled. Particularly, the contact member is placed at the contact position with the ink-permeable of the circumferential wall while the stencil sheet is peeled off at the stencil discharging operation and subsequently at the stencil attaching operation, the contact member is placed at the contact position with the ink-permeable of the circumferential wall while the stencil sheet is attached onto the rotary cylindrical drum, whereby ink drawn out through the ink permeable portion of the circumferential wall to the outer peripheral surface thereof can be removed during the process of the stencil attaching operation from the stencil discharge operation.